File system stange behavior

[daniel]

My hardware

 Pentium(R) 4 CPU 1.90GHz
 RAM 1048560K bytes DDR PC2100
 ad0: 76319MB <WDC WD800BB-00CAA0> [155061/16/63] at ata0-master UDMA100
 motherboard ASUS PAB266-E

 I have it with a 4.5 stable upgraded to 4.7 stable with cvsup
 After I discover the problem of which I talk below, I reinstalled all the 
computer with 4.8 stable, but this was not a solution to my problem.
 There are some weird behavior on the file system.
 I discover it with the security run output and his heading setuid diffs:
 Some files cannot be accessed by the find of the command.
 there are some directory corruption on the file system.

 for example a exit of it:

 find: /usr/ports/security/libfwbuilder/Makefilÿ: No such file or directory

the file exist but the directory is corrupted
if I do an odd -t a on the directory I've got the character FF instead off E
When I am in this situation I can't do anything with theses files , rm find 
etc ... cannot find them. There are always an error when I try to access 
the files referenced in the directory.
But this behavior is not permanent. I can have it for 15 days and after 
that I find again my directory and files ok, without doing anything

Another thing : one time I 've got some rights on files who has been 
modified too. In this case it was possible to put the right rights on them.

At last the system reboot frequently ( every month in average ) with 
inconsistency in the file system. I must run fsck to repair. Since I am in 
4.8 the system always reboot but without inconsistency in the file system.

two error different for the reboot I found in dmesg.boot
    panic: ufsdirhash_findfree: free mismatch
and
    Fatal trap 12: page fault while in kernel mode

 I must say that I have the same configuration on another computer who work 
well for years ago.

 I don't know what part of hardware is in charge of this problem. If 
someone have a clue for me Thanks

 Daniel Madaoui daniel at hackywhacky.com